Control of Gene Expression

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Control of Gene Expression More about bacteria!

Now part of the rest of the bacteria chromosome can be transferred to another bacteria cell: Recombination exchanges segments of DNA.

Why would a bacteria want to control gene expression anyway? In order to adjust to the changing environment. For example: Amino acid, Tryptophan (found in chicken, turkey, fish, soybeans, etc.) E. coli can make their own tryptophan, but are they going to bother making their own when Thanksgiving rolls around?! But first…some VOCABULARY!

The entire stretch of DNA required for enzyme production. Operon The entire stretch of DNA required for enzyme production. Includes the operator, promoter and genes they control.

Promoter Region where RNA polyermase binds

Operator Acts as an “on-off switch” Region between the promoter and the first gene

Repressor Protein that binds to the operator and blocks the attachment of RNA polymerase

Corepressor A small molecule that cooperates with a repressor protein to switch an operator off

Regulatory Gene The gene that produces repressors

Inducer A molecule that inactivates the repressor

Now let’s put it all together!

How do all the parts interact? NO tryptophan in environment: Repressor does not bind to the operator RNA polymerase attaches Enzymes are made that make tryptophan

What happens if we just ate some turkey?! Tryptophan in the environment: Tryptophan acts as a corepressor and binds to the repressor. The repressor now has the correct shape to bind to the operator. RNA polymerase can NOT attach to the promotor Tryptophan synthesis is STOPPED!

Repressible vs. Inducible Operons Repressible operon: one that is inhibited when a specific small molecule binds to a regulatory protein Normally ON: active Function in anabolic pathways (making) Inducible operon: one that is stimulated when a specific small molecule interacts with a regulatory protein. Normally OFF: inactive Function in catabolic pathways (breaking down)

Inducible operon example… The lac operon contains genes that code for enzymes that break down lactose. Your mom forgot to buy milk: your bacteria are not going to make any enzymes for the breakdown of lactose (OFF)

No milk = operator OFF

Got milk = operator ON

Do you know your vocabulary?! Let’s find out!

Clue #1 The entire stretch of DNA required for enzyme production. Includes the operator, promoter and genes they control.

Operon

Clue #2 Region where RNA polyermase binds

Promoter

Clue #3 Acts as an “on-off switch” Region between the promoter and the first gene

Operator

Clue #4 Protein that binds to the operator and blocks the attachment of RNA polymerase

Repressor

Clue #5 A small molecule that cooperates with a repressor protein to switch an operator off

Corepressor

Clue #6 The gene that produces repressors

Regulatory Gene

Clue #7 A molecule that inactivates the repressor

Inducer